In order to produce hydrocarbon fluids and gas, a wellbore must be completed to a hydrocarbon bearing reservoir. Many times, the hydrocarbon reservoir is a sandstone, and many times these sandstone reservoirs are unconsolidated. Operators have long recognized the advantages of preventing sand production from high rate production wells and unconsolidated reservoirs.
Thus, liners, screens, and gravel packing have been employed in order to control formation sand production. Gravel packing is a completion procedure that is performed to prevent sand production from unconsolidated sandstone formations and high production rate wells. It consists of placing a screen or slotted liner in the wellbore wherein the wellbore may be an open hole or cased hole, then filling the perforation tunnels and the annular area between the screen and the casing or open hole with specially sized, highly permeable gravel pack sand. The formation sand bridges on the gravel pack sand, and the gravel pack sand bridges on the screen. It may be referred to as a "reinforcement device" (two-stage filter) for this reason. This reinforcement device allows for sand free production at most rates.
Many types of wire-wrapped screens are available, including ribbed, all-welded, grooved, and wrapped-on-pipe. The all-welded screen includes the wrapped screen welded to longitudinal wire ribs at each point of contact. Spacer lugs, solder strips, and weld beads are not required and, therefore, the all-welded screen is stronger and more corrosion-resistant; it also has a lower pressure drop, and it will not unravel if the wire is eroded or broken.
The configuration of the openings in all screens is very important. If the sides of the slots are parallel and oriented radially outward, plugging may occur as the small sand grains bridge the slot. To reduce the chance of this occurring, the wire used to wrap the screen is wedge-shaped.
For gravel packing, the gauge of the screen should be small enough to prevent the passage of the gravel-pack sand. Slot width is usually taken as one to five thousandths of an inch smaller than the diameter of the smallest gravel-pack sand grains. The screen diameter should be as large as possible and yet leave adequate room for packing gravel.
Despite these advances, the prior art devices still present numerous problems. Presently, operators are completing in highly deviated wellbores. Thus, this presents the problem of successfully navigating through high angle dog legs. Other problems include cutting out the screen due to erosion of the screen at the slots which allow migration and eventual production of gravel pack and formation sand. Also, the plugging and subsequent permeability reduction that leads to excessive pressure drops is present with the prior art screens. Another problem is the expense of manufacturing prior art screens. Therefore, there is a need for a screen used in high angle wells that will effectively prevent sand production while maintaining productivity.